US3317777A

US3317777A - Electric discharge devices

Info

Publication number: US3317777A
Application number: US303259A
Authority: US
Inventors: Algar Leslie Ernest; Cook Kenneth George
Original assignee: MO Valve Co Ltd
Current assignee: MO Valve Co Ltd
Priority date: 1962-08-23
Filing date: 1963-08-20
Publication date: 1967-05-02
Anticipated expiration: 1984-05-02
Also published as: GB978004A

Description

3,317,777 ELECTRIC DISCHARGE DEVICES Leslie Ernest Alger, Wembley, and Kenneth George Cook, Northwood, Mid'dlesex, England, assignors to The M-O Valve Company Limited, London, England Filed Aug. 20, 1963, Ser. No. 303,259 Claims priority, application Great Britain, Aug. 23, 1962,

Claims. (Cl. 313-182) This invention relates to electric discharge devices.

The invention is concerned in particular with electric discharge devices of the kind having a sealed envelope within which are disposed a pair of main electrodes, providing between them a spark gap, and a trigger electrode, the envelope having a high pressure gas filling and the trigger electrode being arranged so that, with a voltage lying within a range below the static breakdown voltage applied between the main electrodes, a discharge between the main electrodes may be initiated by applying a suitable triggering voltage between the trigger electrode and one of the main electrodes. By the static breakdown voltage is meant the lowest value of voltage applied between the main electrodes for which breakdown would occur between the main electrodes in the absence of a triggering voltage; by a high pressure gas filling is meant a gas filling at a pressure which is higher than that pressure of gas filling for which the static breakdown voltage would have its minimum value with a gas filling of the same composition.

Hitherto, such a device has normally been provided with a filling of nitrogen. We have now found that the performance of such a device may be improved in certain respects by using mixtures of nitrogen with xenon and/or argon instead of nitrogen alone.

By using such a mixture, one or more of the following advantages may be obtained, as compared with cases in which a filling of nitrogen is used:

(a) Reduction of the value of the triggering voltage necessary to initiate a discharge;

(b) Reduction of the delay time between the occurrence of a discharge between the trigger electrode and one or other of the main electrodes and the commencement of the discharge between the main electrodes;

(0) Reduction of the variability of this delay time.

The degree of improvement obtainable varies with the precise composition of the gas mixture, but some improvement may be obtained over a wide range of compositions. Accordingly, in its broadest aspect the invention consists in an electric discharge device of the kind specified in which the gas filling consists essentially of a mixture of nitrogen with xenon and/or argon in which the partial pressure of nitrogen constitutes between and 90% of the total pressure.

For convenience in manufacture it will normally be preferred to use a gas mixture in which only one of xenon and argon is included. Thus, according to one aspect of the invention in an electric discharge device of the kind specified the gas filling consists essentially of a mixture of nitrogen and xenon in which the partial pressure of nitrogen constitutes between and 90% (preferably between and 50%) of the total pressure; according to another aspect of the invention in an electric discharge device of the kind specified the gass filling consists essentially of a mixture of nitrogen and argon in which the partial pressure of nitrogen constitutes between 10 and 70% (preferably between 20 and of the total pressure.

One form of electric discharge device in which the invention may suitably be used will now be described by way of example with reference to the accompanying nited States Patent O drawing, which is an elevation, mainly in section, of the device.

The device has a sealed envelope which includes a ceramic tube 1 opposite ends of which respectively fit within and are sealed-to two

tubular metal members

2 and 3 which respectively have

internal flanges

4 and 5 against which the ends of the tube 1 abut. Within the envelope are disposed a pair of main electrodes 6 andv 7 effectively in the form of a pair of copper cylinders of diameter five mm., which are arranged coaxial with each other and with adjacent ends spaced three mm. apart, the edges of the electrodes 6 and 7 at these ends being rounded in order to prevent undesirable discharge effects. The electrode 6, which is intended to operate as a cathode, is solid and forms an integral part of an elongated member 8 which extends coaxially within the tube 1, while the electrode 7, which is intended to operate as an anode, is hollow and forms an integral part of a tubular member 9 which is secured in the central aperture of the flange 5 and which has an internal diameter of 3.5 mm.

At its end remote from the cathode 6 the member 8 is brazed to a metal cup 10 which fits within and is sealed to the member 2 so as to close one end of the envelope, the member 8 being provided at this end with a flange 11 which bears against the flange 4; the cup 10 has a central aperture in which is sealed one end of a copper pumping stem,12, the member 8 having formed within it a hole 13 which connects the interior of the pumping stem 12 to the interior of the tube 1.

The device also has a trigger electrode 14 in the form of a copper rod of diameter one mm. which is disposed coaxially within the anode 7 with the end of the electrode 14 nearer the cathode 6 lying in the same plane as the corresponding end of the anode 7. A tubular ceramic sleeve 15, having internal and external diameters respectively of one mm. and 3.5 mm., fits closelyiround the electrode 14 and within the hole in the anode 7, the sleeve projecting into the gap between the anode 7 and the cathode 6 for a distance of 0.5 mm. beyond the ends of the anode 7 and the electrode 14. The sleeve 15 is constituted by a projection from a tubular ceramic member 16 which is sealed within the member 3 so as to close the second end of the envelope, the central hole in the member 16 having sealed across it a metal terminal member 17 to which the trigger electrode 14 is secured.

It will be appreciated that the

members

2, 3 and 17 respectively provide external connections for the cathode 6, anode 7 and trigger electrode 14.

During manufacture of the device the envelope is first evacuated and then filled with gas via the pumping stem 12, which is then pinched ofl, the gas filling consisting of a mixture of gases having a composition within the range indicated above and its total pressure being made considerably greater than that for which the static breakdown voltage would have its minimum value with a gas filling of the same composition. Two preferred compositions of gas filling are (A) a mixture of 40% nitrogen and 60% xenon and (B) a mixture of 30% nitrogen and 70% argon. The use of a total pressure of the order of 500 torrs for mixture (A) or 1100 torrs tor mixture (B) results in values of static breakdown voltage in the range 4.5-5.0 kilovolts for devices of the form described above. By way of comparison it may be noted that similar values of static breakdown voltage are obtained when using a filling of nitrogen alone at a pressure of about 350 torrs.

The improvement obtainable by use of the invention in devices of the form described above may be illustrated by the following results obtained in experiments carried out with two individual devices of this form.

For the first device. measurements were first carried out with the envelope filled with the nitrogen-xenon mixture (A) at a total pressure of about 500 torrs. With the anode 7 maintained two kilovolts positive with respect to the cathode 6, then when trigger pulses of amplitude kilovolts and rise time five microseconds were applied between the trigger electrode 14 and the anode 7 so as to drive the former more positive, it was found that breakdown occurred between the trigger electrode 14 and one or other of the main electrodes 6 and 7 when the trigger voltage reached a value in the range 1.5-2.5 kilovolts, and that the delay time between the application of a trigger pulse and the commencement of a discharge between the anode 7 and cathode 6 had values in the range 0.9-1.2 microseconds. The envelope of the device was then re-evacuated and filled with nitrogen at a pres- ,sure of about 350 torrs. The device was then operated under the same conditions as indicated above, and it was found that breakdown occurred between the trigger electrode 14 and one or other of the main electrodes 6 and 7 when the trigger voltage reached a value in the range 3-4 kilovolts, and that the delay time between the application of a trigger pulse and the commencement of a discharge between the anode 7 and cathode 6 had values in the range 1.6-2.4 microseconds.

For the second device the procedure was similar, except that measurements were first carried out with the envelope filled with the nitrogen-argon mixture (B) at a total pressure of about 1100 torrs instead of the mixture (A), and that the applied anode-cathode voltage had a value of one kilovolt instead of two kilovolts. In this case, with the nitrogen-argon fillingit was found that breakdown occurred between the trigger electrode 14 and one or other of the mainelectrodes 6 and 7 when the trigger voltage reached a value in the range 1.5-1.8 kilovolts, and that the delay time between the application of a trigger pulse and the commencement of a discharge between the anode 7 and the cathode 6 had values in the range 0.9-1.0 microsecond; on the other hand, with a plain nitrogen filling it was found that breakdown occurred between the trigger electrode 14 and one or other of the main electrodes 6 and 7 when the trigger voltage reached a value in the range 1.9-2.1 kilovolts, and that the delay time between the application of a trigger pulse and the commencement of a discharge between the anode 7 and cathode 6 had values from two microseconds to above nine microseconds.

We claim:

1. An electric discharge device having a sealed envelope within which are disposed a pair of main electrodes, providing between them a spark gap, and a trigger electrode for initiating a discharge between the main electrodes, the envelope having a high pressure gas filling consisting essentially of a mixture of nitrogen and at least one gas selected from the group consisting of xenon and argon in which the partial pressure of nitrogen constitutes between 10 and 90% of the total pressure.

2. An electric discharge device having a sealed envelope within which are disposed a pair of main electrodes, providing between them a spark gap, and a trigger electrode for initiating a discharge between the main electrodes, the envelope having a high pressure gas filling consisting essentially of a mixture of nitrogen and xenon in which the partial pressure of nitrogen constitutes between and 90% ofthe total pressure.

3. An electric discharge device according to claim 2, in which the partial pressure of nitrogen constitutes between and of the total pressure. 1

4. An electric discharge device having a sealed envelope within which are disposed a pair of main electrodes, providing between thema spark gap, and a trigger electrode for initiating a discharge between the main electrodes, the envelope having a high pressure gas filling consisting essentially of a mixture of nitrogen and argon in which the partial pressure of nitrogen constitutes between 10 and of the total pressure.

5. An electric discharge device according to claim 4, in which the partial pressure of nitrogen constitutes between 20 and 40% of the total pressure.

References Cited by the Examiner UNITED STATES PATENTS 2,414,622 1/1947 Watrous 313-325 X 2,431,226 11/1947 Berkey et al. 313244 X 2,447,377 8/1948 Tognola et al 313-355 X 3,207,947 9/ 1965 Goncz. 3,211,940 10/1965 Hueschen 313-325 X JOHN W. HUCKERT, Primary Examiner.

A. J. JAMES, Assistant Examiner.